The present techniques relate generally to large area signage, lighting and similar displays formed from organic light emitting materials. Specifically, the present techniques provide methods for making color-tunable signs from such materials.
This section is intended to introduce the reader to aspects of art that may be related to aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present techniques. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
A developing trend in circuit and display technology involves the implementation of electronic and opto-electronic devices that take advantage of electrically active organic materials. These devices provide low cost, high performance alternatives to silicon-based electronic devices. One such device is the organic light emitting diode (OLED). OLED's are solid-state semiconductor devices, which implement organic semiconductor layers to convert electrical energy into light. Generally, OLEDs are fabricated by disposing multiple layers of thin films made from electroluminescent organic materials between two conductors or electrodes. The electrode layers and the organic layers are generally disposed between two substrates, such as glass or plastic. The OLEDs operate by accepting charge carriers of opposite polarities, electrons and holes, from the electrodes. An externally applied voltage drives the charge carriers into the recombination region to produce light emissions. Unlike many silicon based devices, OLEDs can be processed using low cost, large area thin film deposition processes which allow for the fabrication of ultra-thin, light weight lighting displays. Significant developments have been made in providing general area lighting implementing OLEDs.
Large area OLED devices typically combine many individual OLED devices on a single substrate or a combination of substrates with multiple individual OLED devices on each substrate. Groups of OLED devices are typically coupled in series and/or parallel to create an array of OLED devices which may be employed in display, signage or lighting applications, for instance. For these large area applications, it may be desirable to create large light emitting areas in the array while minimizing the areas that do not produce light due to defects.
Generally, a device is formed from a single layer that may contain multiple OLED devices arranged side-by-side, as the electrode material used for cathodes may not be transparent. To form different colors or to increase reliability in the devices, different devices may be connected across the surface of the device in a serial or parallel fashion. However, while the combination of many interconnected devices in the substrate layer may increase the reliability of a large area OLED device, it may limit the minimum size of an individual feature. This may provide a coarse “pixel” or large non-emissive areas that may make the production of fine features in a sign or picture difficult to display. Furthermore, the coarse pixel may be visible to the human eye, making color blending difficult, when uniform appearance is desired. Finally, the interconnections will increase the cost of a display panel, which may make it impractical for low end applications. Similarly, a pixilated display having fine features may be made from individually addressable points, connected in either a passive or an active matrix, but the complexity of the resulting panel and, thus, the cost, may limit the use to high end applications.